[Columbine]

Seconding MMM's comment. Kyoto is just small enough and interesting enough that you won't need a car. I walked pretty much most of it over a few weekends but you won't want to do all of it in under a week. You'll get temple head. Plus parking is a pain in the proverbial to find, so i'd stick to pub. trans. if I were you.

Asides from the dome, park and museums, Hiroshima is pretty much a bog-standard city. You could easily do that in a day, or two-three if you wish to see Miyajima as well (1 hr apox. out of the city by tram and ferry but well worth seeing). In all probabilities, unless you're traveling to the back of beyond, you'll be better off doing it by train and bus.